Apparatus for electrical testing



May 7, 1935.

R. o. HURD ET AL APPARATUS FOR ELECTRICAL TESTING Original Filed July l, 1931 2 Sheets-Sheet l fiqy C. Hard BY Thomas f. Had 'lhfl ATTOR EY HO VOLTS y 1935- f R. ol HURD =:r AL 5 APPARATUS FOR ELECTRICAL TESTING' i Original Filed July l, 1931 2 sheets-sheet 2 I20 VOLTS ATTOR EY Patentecl May 7, 1935 QFFICVE m ts;

APPARATUS FOR ELEGIRIC A L TESTING oy oLHrd a T asfl zkhs n Sam. f Francisco, Calf., assignojs to Newton J, Halo,- V

San Francisco, Calif.

'Application July 1, 1931, Serial No. 548,069'

' Renewed .0ctober-16,=1934 mama (elin-zu i The present invention relates to methods and 'caused by such abnormalities as shorting, opening, or varying the electrical relation etc., of tube circuits or elements due to mechanical vibration, thermal conditions within the tube or the presence of gas therein. Particularly Where such changesgoccur intermittently and are of extremely minute duration they are sufficient to cause noise (or flickering and streaking in television'apparatus) when the tube is placed in operation, and yet are extremely difficult of `detection.v m

It is an object 'of the present invention to provide anfimproved method and apparatus for testing for 'such defects, whereby the presence of such defects will cause radio'frequency oscillations to be set up in the testingappara'tus, from -whieh sensible ind'cations of the defect present may be produced.

Another object of the -invention isthe provision of 'apparatus adapted to apply a plurality of -types of tests to such de'viees. Other Objects willappear" hereinafter.

V' A preferred form of apparatus for carrying out'the above Objects is illustratedinthe accompanying drawings forming a partof' this specifica-tion, in which: 1 Q

Figure 1 is adiagram o f the electrical conneccis f the est n p a tus Qr te t f t put, and a portion of the structural, testing appara u and. f s

Pierre 2 i a ntin atio h r of show ng detecti n and dica cn ap ara us crre iqr and powe su p y In'the nre r e rm Qf p ra u here dis- `closed, a plurality of tube socketsare provided fore e vneihe va Qu t p s O tre s L. 213. and 4 to be tested therein and filament, 'current r v h o er volta e fo e c e o t be provided by a plurality of secondaries 5 of tra'nsformerfi. The plate pro g Contacts of all the test. sockets areconnected in gang bylead f! to th is n travein contact e Of the 'esi'lng'switch 9 through approprate resistances Q ea Of Which is hi b a la -naiseend nser H fer he pu mseqf ap rcpr iatey--red ipe; he nla e current to. the various yn s c "cause'variations in' 'the plate current. These tubes without interference with radio-frequency currents in the plate circuit.

I In testingfor Structural defects the traveling contact 8. is thrown to the right connecting the plate of the tube under test, via lead l2 to the primary winding of a radio-frequency transformer l3 and thence via leads M, l, and-l` to one side Iofthe DL C. power supply at 11, the, other side of said power supply being grounded to the frame at l8. The power supply may be of any desired form delivering approximately 250 volts D. C., and is shown as comprising a step-up'transformer, rectifier tube, and filters of conventional types. i A eondenser 2B`shunted across the primary of transformerl3` f forms an oscillatings circuit therewith, in which variations of extremely 'minuteduration in the plate current of the'tube under test set-up -oscil1ations the durat'ion 'of whichaiscontrolled only by the logarithmic'de- -crement, and hence a high frequency oscillating circuit is desirable. In practical operation a frequency-of 1'75 kilooycles has 'been found satisfactory but-any vz riation from this value would obviously affect the result only in degree. f

The gr-idjprong contactsof all the test sockets areigangedfon1ead--|9 Which is connected via -leadlD to the-ieft-hand traveling COntactZI-of main) switeh 9, 'yv-hereby when the switch 9 is thrown to the right, the grid of the tube under -test is grounded-via'lead 22 through resistance -23 and, when switch 9 is thrown to the left is connected via lead 24' to secondary winding25 of transformer Bwhichacts asa C battery. The other elements of the tube under test are connected in the conventional manner as indicated by the-diagram. 1

- T-he output of radio frequency transformer [3 is' coupled through radio frequency' amplifying, `detector ancl audio frequency amplifying stagfes of 40 conventional form,` as shown in the diagraxn; to any device for pr'oducinfg` Sensible indications of variations in the output of' the detector Stage;

in the present disclosure, to the moving coil 38 `:of 'a dynamic t'y-pe loud speaker, the fixed coil '39' of which is supplied with current' from the rec'tifier, as shownj i A tube to be tested`,'-isfplaced in the'te'sting socket 1,*2, 3,101' 4 provided for tubes -of i ts variations, however, are usually of such very minute duration as to be incapable of affecting, either directly or through mere audio frequency amplifcation, the diaphragmof a Speaker or other Sensible indication device, and the present invention is directed to a method and apparatus for rendering such variations perceptible.

For this purpose, the plate circuit of the *tube under test is connected to an oscillating circuit formed by the primary of transformer |3 and.

condenser 26, and even the most instantaneous fluctuations of current in the plate circuit act to set up Oscillations of the selected radio frequency in the primary of transformer I3. Such Oscillations terminate by decay, but persist appreciably longer than the plate current Variation initiating them, and are of `sufficient duration to operate sensible indicating devices in* cases where their originating current Variation would not have been. known fact that the force required to produce a given movement varies inversely as the square of the time during which it is exerted, and that 'therefore the current required to produce an audible movement of a speaker diaphragm varies inversely as the square of the time during which it is applied. It is thus clear that if the duration of an impulse to the Sensible indication device can be doubled, an amplitudeequalto the square root of its original amplitude will be sufiicient to produce the same effect thereon,

and it is by taking advantage of this principle that the 'present invention obtains its result. V

Oscillations so caused in the primary of transformer induce similar Oscillations in the resonated secondary thereof, which are amplified by successive radio frequency stages of conventional design, as shown, rectified in a detector Stage 21, and act through optional audio frequency stages of amplification to operate the diaphragm of the Speaker through coil 38. V 7 V If no defects have been made apparentin the progress of the test to this point, the tube is then vibrated either manually or by suitable mechanical means, when additional defects such as those due to looseness or insufiicient support of elements or the intermittent shorting or opening of circuits within the tube will be indicated in the same manner by the same means above set forth. f If no defects are made apparent by these tests, a tube giving a satisfactory emission may be considered satisfactory for use in a' radio or television receiving set, since all defects capable of producing interference in such apparatus have been demonstrated to be absent. All tubes to be used in such apparatus, including rectifier tubes, should be so tested, for a tube functioning in the audiofrequency stages of a 'receiver may be wholly free from defects capable of producing audio frequency disturbances and yet may create disturbances which will be picked up by the adjacent radio frequencystages and become audible as noise in the speaker. --Similarly,

a rectifier tube so placed in the circuit as to be incapableof transmitting audio' frequency disturbances to the speaker may create disturbances which will be picked up by nearby radio frequency stages'and thus appear, as noise Lin the Speaker. l v

Each tube is also tested by an A, C. voltmeter adapted to be coupled into the platecircuit of the tube under test'by throwing switch 9 to the left. The right traveling contact 8 of this switch is, as above setforth, connected to :the

This is clear from the well plate prong contacts of all the test sockets, and thus the throwing of this switch to the left connects the plate of the tube under test via lead 30 to the primary winding of transformer 3l and thencevia leads 32, 33, 34, l5, and |6 to power supply. The secondary winding of transformer 3! is connected by leads to any well known type of hypersensitive A. C. voltmeter. A satisfactory type of voltmeter for this purpose consists of a D. C. voltmeter having a 'dry pile rectifier built in, together with the usual means for bringing the meter into the proper range.

The left hand traveling contact 2 of switch 9 'being connected to the grid prong, contacts all of the test sockets, and the throwing of the switch serves to connect the grid of the tube under test via lead 36 to a secondary winding 31 of transformer 6.

This arrangement is merely illustrative and any well known type of meter test may be substituted therefor.

separate metering circuits, functionally associated with the structure testing apparatus, are provided fordetermining the emission of the various types of rectifier tubes.

A test Socket is provided for receiving a full Wave rectifier tube 40 which receives its filament current from a secondary winding 4| of transformer 6. The plates of the tube are connected via leads 42, 43, 44, 45, 46, and 41 to opposite ends of a secondary 48 of transformer 6 supplying the proper alternating current voltage therefor, and from a central tap thereon through a D. C. milliammeter 49, containing a shunted resistance, through resistance 50 to the filament circuit. Switches 5! and 52 are provided in the circuitof each plate, either of which may be opened by throwing key 53 thereof up or down to test the efficiency of each plate separately.

Therectifier tube 40 having been placed in the testing socket, jany disturbances created within thervgrectifier tube either spontaneously or upon vibration thereof will be picked up and made audible in the Speaker, the mere proximity of the circuits being suflicient to effect reception of these disturbances if the circuits of the primary of transformer 3 are within a few inches of the tubes. Furthermore, by throwing key 53 first in one direction and then in the other, one plate and then the other may be cut out of circuit and the specific defective element causing the disturbance thus determined. If it is desired to locate the specific defective element in multiple element tubes such as shown at I, 2, and 3, similar switches may be provided for cutting out the various elements selectively'.

A half-Wave rectifier tube 54 may be similarly tested, its single plate being connected through cut out switch 55 via lead 45 tosecondary 48 and thence by the central tap through voltmeter 49 and-resistance 56 to the filament circuit of the tube, supplied by secondary winding 51 of transformer 6.

Means are also provided for testing raytheon tubes, such as shown at 58, the cathodes of which are shunted by bufier condensers 58 and connected via leads 43 and 46 through switches 5| and 52 through secondary 48, voltmeter 49, and 'resistance 60 via lead 6| to the anode.

ltis obvious that the method of testing herein `disclosed could be carried out with apparatus diifering materially from that herein disclosed. For instance, by providing a separate source of 'plate voltage for the tube to be tested, it would be possible to connect the plate of said tube and one side of said plate voltage line to the antenna and ground connections of any type of radio receiving set, and by properly tuning the set practice the method here disclosed.

Furthermore, it is not necessary for an actual physical connection to be provided between the tube under test and the detector, since any relation Whereby the disturbances may reach the oscillating circuit will sufiice, as is illustrated by the fact that disturbances in tubes situated as tubes 40, 54, and 58, will be picked up and rendered audible in the Speaker, or by the fact that if the condenser- 26 is eliminated, oscillations will nevertheless be set up in the resonated secondary circuit and the same result secured.

. Even with both condensers eliminated, the distributed capacity of the windings and tube would be sufiicient in many cases to set up the necessary oscillations.

It is therefore obvious that variations in the 'apparatus disclosed will occur to those skilled 'for prolonging the effect of transient impulses in a tube, comprising an oscillatory circuit cooperatively associated therewith, and means for rectifying and conveying to said mechanism oscillations produced by defects in a tube under test.

2. In vacuum tube testing device, means for simulating the effect of adefective tube's operation in a receiving set comprising reproducing mechanism, a detector of radio frequency oscil- V lations cooperatively associated therewith, means for prolonging the effect of transient impulses in a tube, comprising an oscillatory circuit including said tube, and means for picking up and conveying to said detector, oscillations produced by defects in a tube under test.

3. In vacuum tube testing apparatus, the combination of energizing circuits, means for connecting a tube to be tested in said circuits, and means comprising an oscillating circuit having reproducing mechanism associated therewith for producing audible indications of disturbances caused by any element of the tube under test.

4. In a vacuum tube testing apparatus, means for audibly simulating the effect of a defective V with for indicating defects in a tube under test,

and electrical means for prolong'ing the effect upon said mechanism of each individual electrical disturbance occurring in the tube under l test.

ROY O. HURD. THOMAS E. HODGKINSON. 

